Engine emission control systems may utilize various exhaust sensors. One example sensor may be referred to as a Particulate Matter (PM) sensor, which indicates PM mass and/or concentration in the exhaust gas. In one example, the PM sensor may operate by accumulating soot particles over time and providing an indication of the degree of accumulation as a measure of exhaust soot levels. Once full, the sensor may be regenerated by removing the stored soot at increased temperatures. The temperature may be regulated via a sensor heater, with current feedback provided to maintain proper temperatures.
The inventors herein have recognized, however, that over-temperature and under-temperature conditions may still occur due to lack of current feedback, or other inaccuracies and variation in operating conditions. For example, changes in exhaust flow temperature can affect sensor temperature to become too high, possibly degrading the sensor, or too low, resulting in ineffective soot removal and thus sensor reading inaccuracies.
As such, at least some of the above issues may be addressed by controlling a particulate matter sensor heater by operating the heater to burn-off soot accumulated on the sensor, and adjusting the heater level based on sensor output generated during the heater operation.
For example, during a soot removal operation, the sensor output can provide insight into the sensor temperature, as opposed to the soot level of the engine exhaust. During sensor burn-off, the conductivity or resistivity of the sensor may change with the temperature of the sensor thus enabling the sensor to indicate whether the sensor is operating with the temperature, too high, or too low. In this way, it is possible to operate the heater more efficiently, thus avoiding excess heating that can waste energy (and thus degrade fuel economy) and/or degrade sensor performance.
Note that there are various PM sensor readings that may be used, such as conductivity, resistivity, etc., and further the sensor output may be processed in various ways, such as using pull-up or pull-down circuits, amplifiers, etc.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.